高压对氮化硼纳米管的几何结构、电子结构和光学性质的影响

运用密度泛函理论平面波赝势方法(PWP)和广义梯度近似(GGA),计算研究了纳米管BN(5,5)在不同压力条件下的几何结构、电子结构和光学性质. 在高压条件下管口形状发生了较大的变化. 与闪锌矿结构BN比较分析发现两种结构间存在一些性质上的差异：首先,在外压力作用下,BN(5,5)纳米管的带隙随压力增大而减小,变化率为-0.01795eV/GPa,而闪锌矿结构BN随压力增大而增大;其次光吸收谱在压力条件下,没有和闪锌矿结构BN一样发生“蓝移”,相反在红外方向有所拓展;但纳米管BN(5,5)电子的转移方向和 关键词： 氮化硼纳米管 密度泛函理论(DFT) 电子结构     

(AlB2)m (m=1~6) 团簇的几何结构和电子性质

采用密度泛函理论(DFT)中的B3LYP方法得到了(AlB2)m团簇的平衡几何结构. 计算并分析了基态掺杂团簇的平均结合能、电离势、能隙和前线分子轨道. 结果表明：掺杂团簇(AlB2)m (m=1~6)整体上具有较高化学活性,(AlB2)5团簇具有金属特征. Al原子总是向团簇外围扩散并且以配位数较少的方式与主团簇结合,团簇表现出以AlB2分子为基元生长的迹象. B-Al键长大于B-B键长. 电荷总是从Al原子转移到B原子. (AlB2)m团簇中B原子的2p轨道在成键中起主要作用,并使(AlB2)m团簇趋于形成离域π键.     

内嵌水二聚体富勒烯(H2O)2@C84的基态性质与光谱特性

采用密度泛函B3LYP方法以6-31G为基组研究了富勒烯D_(2d)(23)-C_(84)和内嵌水二聚体富勒烯(H_2O)_2@D_(2d)(23)-C_(84)的中性、阴离子及阳离子基态几何结构、稳定性、电荷分布、能量、电偶极矩、能隙、红外及拉曼光谱特性;用含时的TD-B3LYP方法研究了富勒烯C_(84)和内嵌水二聚体富勒烯(H_2O)_2@C_(84)的紫外-可见吸收光谱.研究结果表明:水二聚体的加入导致了富勒烯分子的对称性降低、偶极矩增加,体系能隙减小,同时水二聚体的氢键键长减小.另外,水二聚体的加入改变了富勒烯分子的红外和拉曼光谱特征,如谐振频率的移动以及红外和拉曼峰的增强或减弱.研究结果显示水二聚体的加入致使富勒烯分子的最大激发波长发生红移,对其它激发波长的位置以及振子强度也产生影响,如光学活性(振子强度不为0)的激发态成为光学非活性(振子强度为0)的激发态或者光学非活性的激发态成为光学活性的激发态;同时研究发现C_(84)存在能量简并的激发态,而(H_2O)_2@C_(84)并没有能量简并的激发态;虽然水二聚体的加入影响富勒烯分子的激发特性,但计算结果显示C_(84)和(H_2O)_2@C_(84)经展宽后的紫外-可见光谱轮廓基本一致.该研究可以为将来的实验光谱测量提供理论依据,也可以为内嵌水二聚体富勒烯的合成和应用提供理论指导.     

Ni掺杂MgF2电子结构和光学性质的第一性原理研究

基于密度泛函理论(DFT) 的第一性原理平面波超软赝势方法,计算了过渡金属Ni不同比例（16.67%,12.5%,8.33%,6.25%）掺杂MgF2晶体的几何结构、电子结构和光学性质。通过对比发现,由于Ni原子的掺入, 体系的禁带宽度减小且能带中出现中间杂质带。另外, 介电函数虚部以及吸收光谱图中均出现双峰结构,结合前人的计算给出了详细的物理机制。上述现象,揭示了Ni掺杂MgF2 体系在光学元器件方面的潜在应用。     

Ni掺杂MgF2电子结构和光学性质的第一性原理研究

基于密度泛函理论(DFT) 的第一性原理平面波超软赝势方法,计算了过渡金属Ni不同比例（16.67%,12.5%,8.33%,6.25%）掺杂MgF2晶体的几何结构、电子结构和光学性质。通过对比发现,由于Ni原子的掺入, 体系的禁带宽度减小且能带中出现中间杂质带。另外, 介电函数虚部以及吸收光谱图中均出现双峰结构,结合前人的计算给出了详细的物理机制。上述现象,揭示了Ni掺杂MgF2 体系在光学元器件方面的潜在应用。     

压强下TaB和TaB2力学和超导性质的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法, 在广义梯度近似下研究了TaB和TaB2在不同压强下的弹性常数、原子结构、电子结构以及超导性质及其对两者物理性质不同进行了比较. 计算结果表明随着压强的增加, 弹性常数和体弹模量随之增加, 而相对晶格常数a/a0, b/b0, c/c0和相对体积V/V0随压强增加而减小. 在高压下, TaB沿着a轴方向的压缩性要比b轴方向大, 而b轴方向的压缩性要比c轴方向大; TaB2是沿着c轴方向的压缩性要比a轴方向的压缩性大. 电子结构分析表明TaB2的原子态杂化程度比TaB的原子态杂化程度要高, 这与TaB2的体弹模量比TaB的体弹模量高的结果相一致. 依据Bardeen-Cooper-Schrieffer超导理论, TaB和TaB2费米能级处态密度的值随着压强的增加而降低, 说明它们的超导转变温度Tc随着压强的增加而降低.     

高压下氧化镉弹性性质、电子结构和光学性质的第一性原理研究

 运用基于密度泛函理论的平面波赝势方法（PWP）,计算研究了氧化镉NaCl结构（B1结构）和CsCl结构（B2结构）在不同压力条件下的几何结构、弹性性质、电子结构和光学性质。交换关联能分别采用广义梯度近似（GGA）和局域密度近似（LDA）。通过比较计算和实验得到的晶格常数和体模量不难发现,LDA的计算结果更符合实验值。在高压的作用下,两种结构的导带能级有向高能级移动的趋势,而价带能级有向低能级移动的趋势,因此直接带隙变大。同时,对照态密度分布图及高压下能级的移动情况,分析了CdO两种结构在高压作用下的光学性质。     

高压下ZnS的电子结构和性质

运用密度泛函理论体系下的平面波赝势(PWP)和广义梯度近似(GGA)方法，计算研究了闪锌矿结构的ZnS晶体在不同的外界压强下的电子结构. 通过分析发现，随着外界压强的增大，晶格常数和键长在不断缩小，从S原子向Zn原子转移的电荷越来越少，Zn—S键的共价性逐渐增强，Zn原子和S原子的态密度都有不同程度的变化，而且还有向低能量移动的趋势. 当外界压强达到24GPA时，ZnS从直接带隙半导体变成间接带隙半导体，而且随着压强的增大，间接带隙逐渐变小，直接带隙逐渐增大. 关键词： 闪锌矿结构 态密度 能带结构 密度泛函理论     

(GaMn)As体系中Mn无序对其电子结构及磁性影响的第一性原理研究

关键词：     

萤石结构TiO2的电子结构和光学性质

利用第一性原理计算了立方相萤石TiO₂的晶胞参数,能带结构和电子态密度.结果显示萤石TiO₂属于间接带隙半导体材料,其间接禁带宽度(Γ→X)E_g为2.07eV,比常见的金红石和锐钛矿TiO₂的禁带宽度窄.为了更清楚地了解萤石的光学性质,利用Kramers-Kronig色散关系,分别对萤石和金红石TiO₂的复介电常数、吸收率等参数进行了计算,并将二者结果做了 关键词： 2')" href="#">萤石结构TiO₂ 密度泛函理论 能带结构 光学性质     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利，属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV)，表明在较低温度下，CO分子在Pu (100)表面会发生离解吸附，离解的C，O原子将占据能量最低的穴位.     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利,属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV),表明在较低温度下,CO分子在Pu (100)表面会发生离解吸附,离解的C,O原子将占据能量最低的穴位. 关键词： 密度泛函理论 Pu (100) CO 分子和离解吸附     

First-principles study of mechanical stability and thermal properties of MNNi3 （M=Zn,Mg,Al） under pressure

The mechanical stability,elastic,and thermodynamic properties of the anti-perovskite superconductors MNNi 3（M=Zn,Mg,Al） are investigated by means of the first-principles calculations.The calculated structural parameters and elastic properties of MNNi 3 are in good agreement with the experimental and the other theoretical results.From the elastic constants under high pressure,we predict that ZnNNi 3,MgNNi 3,and AlNNi 3 are not stable at the pressures above 61.2 GPa,113.3 GPa,and 122.4 GPa,respectively.By employing the Debye model,the thermodynamic properties,such as the heat capacity and the thermal expansion coefficient,under pressures and at finite temperatures are also obtained successfully.     

Novel Tb(III) complexes with two different structures of phosphine oxides and their properties

Novel Tb(III) complexes with two different structures of phosphine oxide ligands and three β-diketonates were synthesized. Characteristic of the excitation spectra mainly depend on the substituents of β-diketonates, and remarkable correlation among molecular structures, maximum wavelengths and emission intensity could be found. Namely, the shorter the maximum wavelengths when electron-donating groups are substituted in β-diketonates, the larger the emission intensity. These results were explained on the basis of extent of back energy transfer from excited Tb(III) ions to the ligand. From the analysis of the branching ratio of emission spectra, that is defined as the ratio of the intensity of the electric-dipole transition to the magnetic-dipole transition, complex 2 with β-diketonates having small substituent (methyl group) has more asymmetric ligand fields than others. It was found that introduction of two different phosphine oxide was effective for increasing solubility of Tb(III) complexes.     

Structural, elastic, phonon, and electronic properties of MnPd alloy

The structural, elastic, phonon, and electronic properties of MnPd alloy have been investigated by using the first-principles calculations. The calculated lattice constants and electronic structure are in good agreement with the experimental results. The microscopic mechanism of the diffusionless martensitic transition from the paramagnetic B2 (PM-B2) phase to the antiferromagnetic L1₀ (AFM-L1₀) phase through the intermediate paramagnetic L1₀ (PM-L1₀) phase has been explored theoretically. The obtained negative shear modulus C′= (C₁₁-C₁₂)/2 of the PM-B2 phase is closely related to the instability of the cubic B2 phase with respect to the tetragonal distortions. The calculated phonon dispersions for PM-L1₀ and AFM-L1₀ phases indicate that they are dynamically stable. However, the AFM-L1₀ phase is energetically most favorable according to the calculated total energy order, so the PM-L1₀ !AFM-L1₀ transition is caused by the magnetism rather than the electron–phonon interaction. Additionally, the AFM-L1₀ state is stabilized through the formation of a pseudo gap located at the Fermi level. The calculated results show that the CuAu-I type structure in the collinear antiferromagnetic state is dynamically and mechanical stable, thus is the low temperature phase.     

Structural, elastic, phonon and electronic properties of a MnPd alloy

The structural, elastic, phonon and electronic properties of a MnPd alloy have been investigated using the first-principles calculation. The calculated lattice constants and electronic structure agree well with the experimental results. The microscopic mechanism of the diffusionless martensitic transition from the paramagnetic B2 (PM-B2) phase to the antiferromagnetic L10 (AFM-L10) phase through the intermediate paramagnetic L10 (PM-L10 ) phase has been explored theoretically. The obtained negative shear modulus C′= (C11-C12)/2 of the PM-B2 phase is closely related to the instability of the cubic B2 phase with respect to the tetragonal distortions. The calculated phonon dispersions for the PM-L10 and AFM-L10 phases indicate that they are dynamically stable. However, the AFM-L10 phase is energetically most favorable according to the calculated total energy order, so the PM-L10 →AFM-L10 transition is caused by the magnetism rather than the electron-phonon interaction. Additionally, the AFM-L10 state is stabilized through the formation of a pseudo gap located at the Fermi level. The calculated results show that the CuAu-I type structure in the collinear antiferromagnetic state is dynamically and mechanically stable, thus is the low temperature phase.     

Elastic,mechanical, electronic properties and hardness of Nb2AsC from first principles

The study aims at the elastic, mechanical, electronic properties and hardness of Nb₂AsC using first principles based on the density functional theory method within the generalised gradient approximation. The calculated lattice parameters of Nb₂AsC are in good agreement with the experimental data. The five independent elastic constants are firstly calculated as a function of pressure, and our results indicate that it is mechanically stable in the applied pressure. The elastic anisotropy is examined through the computation of the direction dependence of Young's modulus. The pressure dependences of the bulk modulus, shear modulus, average velocity of acoustic waves and Debye temperature of Nb₂AsC are systematically investigated. The band structure and density of states are discussed, and the results show that the strong hybridisations C p–Nb d and As p–Nb d would be beneficial to the structure stability of Nb₂AsC. Based on the Mulliken population analysis, the hardness of Nb₂AsC is predicted.     

萤石结构TiO2的电子结构和光学性质

利用第一性原理计算了立方相萤石TiO₂的晶胞参数，能带结构和电子态密度.结果显示萤石TiO₂属于间接带隙半导体材料，其间接禁带宽度(Γ→X)E_g为2.07eV，比常见的金红石和锐钛矿TiO₂的禁带宽度窄.为了更清楚地了解萤石的光学性质，利用Kramers-Kronig色散关系，分别对萤石和金红石TiO₂的复介电常数、吸收率等参数进行了计算，并将二者结果做了